The present invention relates to a closure device for a withdrawable rack or module frame in which an electric switch, such as a power circuit breaker, can be inserted.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
In the following description, reference is made in general to “power circuit breaker” which should be understood in a generic sense to cover any type of electric switch for insertion into a withdrawable rack.
A closure device, which is also known as shutter, for a withdrawable rack is provided to prevent personnel in the vicinity of the withdrawable rack from accidentally touching exposed live contacts, such as contact blades located on the rear wall of the withdrawable rack, when the withdrawable rack is open, i.e., when a power circuit breaker is not inserted. Otherwise, personnel may receive a lethal electric shock when touching the exposed contacts. As protection from electric shock, two or more plates with openings are provided, wherein in a closed position of the closure device the openings of each plate are covered by at least one of the other plates, so that the plates effectively cover the contacts or contact blades. Conversely, when the closure device assumes an open position, the openings of the plates are in alignment and the entire plate arrangement can slide over the contact blades. Alignment of the openings can be realized by moving at least one plate with respect to the other plates, using a mechanism which is operated not by service personnel but by a power circuit breaker as it is inserted. Once the power circuit breaker is inserted, there is no risk for service personnel of touching the contact blades.
German Pat. No. DE 103 42 596 B3, published May 12, 2005, describes such a mechanism for a closure device. The mechanism includes two V-shaped linkage assemblies, wherein the legs of each linkage assembly are interconnected by a hinge for rotation. The hinge allows the linkage assembly to spread apart by increasing the angle between the legs. The free end of one of the legs of each linkage assembly is connected with a movable plate, whereas the other leg of each V-shaped linkage assembly is stationary. Ends of a telescoping bar with a variable length are attached to the corresponding hinges. The hinges move perpendicular to the insertion direction of the power circuit breaker, when the linkage assembly is spread apart, thereby increasing the distance between the hinges. This type of closure device suffers shortcomings because the telescoping bar must be extended during transition from a closed state to the open state and because during insertion the power circuit breaker applies pressure upon the telescoping bar as the telescoping bar telescopes out and moves perpendicular to the insertion direction of the power circuit breaker. As a consequence relatively high friction forces are generated which are further amplified by the substantial lever effect produced by the V-shaped linkage assembly.
It would therefore be desirable and advantageous to provide an improved closure device for a withdrawable rack, to obviate prior art shortcomings and to enable a low-friction operation.